1. Field of the Invention
The present invention relates to a method for detecting a contact state of a resistive touch panel device, a resistive touch panel device, and a display device, and more particularly to a method for detecting a contact state of a resistive touch panel device, a resistive touch panel device and a display device capable of detecting a distance between two points pressed simultaneously.
2. Description of the Related Art
A resistive touch panel device has a configuration in which a resistive film to be pressed and a resistive film opposite thereto are provided on surfaces facing each other of a substrate to be pressed and a substrate opposite thereto, respectively, such that the substrates are arranged opposite to each other at intervals. When the substrate to be pressed is touched from the surface opposite to the surface on which the resistive film to be pressed is formed and thereby bent, the resistive film to be pressed and the opposite resistive film will be locally made into contact, and the resistive film to be pressed and the opposite resistive film will be brought into electrical conduction at a contact point therebetween. In such a resistive touch panel device, a driving circuit alternately applies a voltage to between both ends of the resistive film to be pressed and both ends of the opposite resistive film, and detects the position of the contact point as a touched position.
The above-described type of resistive touch panel device derives the contact point through arithmetic processing based on the premise that the number of touched portions (press portions) is one. Accordingly, when more than one point is pressed simultaneously, the above-described pair of the resistive films will be brought into conduction at more than one contact point, and thereby false detection will be made that a midpoint therebetween has been pressed. For example, Jpn. Pat. Appln. KOKAI Publication No. 8-241161 discloses a technique of determining that more than one point has been pressed based on a phenomenon that a resistance between the both ends of the above-described resistive film to be pressed will decrease when more than one point is pressed.
A touch panel device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-241161 determines that a plurality of points have been pressed for the purpose of preventing error detection. On the other hand, as an input method of providing a variety of operations, a touch panel device has been desired that acquires information that more than one point has been simultaneously pressed as being significant. It is particularly meaningful to detect information on a distance between two points when the two points have been simultaneously pressed.